Lubricating compositions containing 2-benzothiazyl-n, n-dialkyldithiocarbamates



United States Patent LUBRICATING COIVIPOSITIONS CONTAININGZ-BENZOTHIAZYL N,N-- DIALKYLDITHIO- CARBAMATES No Drawing. ApplicationJuly 3, 1951, Serial No. 235,092

21 Claims. (Cl. 252-33.4)

This invention relates to hydrocarbon oil compositions having improvedanti-corrosive properties. More particularly it relates to lubricatingoil compositions containing small amounts of2-benzothiazyl-N,N-dialkyldithiocarbamates.

Metals in prolonged contact with hydrocarbon oils ordinarily undergoconsiderable corrosion due .to the insufficient protection which suchoils afford metals against the action of oxygen or water or of corrosivecompounds contained in the oils themselves. This is especially true inthe case of petroleum products,.which tend to undergo oxidation in thepresence of air with the formation of acidic compounds and in whichcorrosive sulfur-containing compounds may be either originally presentor introduced during the .refining process It is, therefore, commonpractice to add to lubricating and preservative oils various types ofcompounds for imparting anticorrosiveness, particularly to ferrousmetals and copper. A large number of different compounds have beenemployed for this purpose, one of the most elfective beingZ-mercaptobenzothiazole, Which functions both as a corrosion inhibitorand as an antioxidant. However the compounds which have been employedheretofore are not sufliciently effective to impart the degree ofanticorrosiveness required in many cases, and the effect obtainable byZ-mercaptobenzothiadole, for example, is furthermore limited by theslight solubility of the compound in hydrocarbon oils.

A principal object of the present invention is to provide an improvedlubricating oil having excellent anticorrosive properties. Anotherobject is to provide an improved hydraulic oil capable of meeting therigorous specification requirements for aircraft hydraulic oils. Stillanother object is to provide an improved lubricating and preservativeoil which affords prolonged protection against metal corrosion in dampor humid atmospheres.

In accordance with our invention a hydrocarbon oil composition havinggreatly improved corrosion inhibiting properties in contact with metalsis obtained by adding to such composition a small amount of aZ-benzothiazyl- N,N-dialkyldithiocarbamate. Compounds of this class maybe represented by the following formula bon atoms, or higher, andpreferably from one to about 2,785,129 Patented Mar. 12, 1957 six carbonatoms. Examples of such compounds which may be mentioned include2-benzothiazyl-N,N-ditertiarybutyldithiocarbamate, 2-benzothiazyl-N,Nethylhexyldithiocarbamate,2-benzothiazyl-N,N-methylisopropyldithiocarbamate,2-benzothiazyl-N,N-diamyldithiocarbamate, and so forth. A very suitablecompound of this type, for example, is2-benzothiazyl-N,N-diethyldithiocarbamate. This compound is commerciallyavailable under the trade name of Ethylac.

We have found that hydrocarbon oil compositions containing small amountsof the above compounds have greatly improved anticorrosiveness tometals, particularly to ferrous metals and copper, as compared with suchcompositions containing other anticorrosive agents heretofore employedfor this purpose. In comparison with the widely used compoundZ-mercaptobenzothiazole, for example, they impart superioranticorrosiveness and equivalent oxidation stability to thecompositions. In addition they have greatly improved solubility andchemical stability.

These compounds impart improved anticorrosiveness to hydrocarbon oilseven when present in small amounts. In lubricating and preservative oilsthey are preferably employed in amounts between about 0.005 to about 0.2percent by weight, although somewhat smaller or larger amounts up totheir limit of solubility may be employed if desired.

Lubricating oils containing these compounds may also contain otheradditives of the usual types so far as no incompatibility exists, as forexample anti-wear agents, viscosity improvers, oxidation inhibitors,other corrosion inhibitors, and so forth, as well as metal soaps orother thickening agents either in minor amounts or in grease formingproportions.

The anticorrosive properties of hydrocarbon oils containing2-benzothiazyl-N,N-dialkyldithiocarbamates has been demonstrated byadding a typical compound of this class,2-benzothiazyl-N,N-diethyldithiocarbamate, to a number of differenthydrocarbon oils and determining the corrosiveness of the resultingcompositions to metals by means of standard tests. While2-benZothiazyl-N,N-diethyldithiocarbamate has been used in the followingexamples for purposes of illustration, it is to be understood that anyof the compounds of this class described above may be used if desired.

In accordance with our invention a superior hydraulic oil having a highdegree of anticorrosiveness to metals was developed by the addition of2-benzothiazyl-N,N-diethyldithiocarbamate to a base oil containing otheradditives for imparting oxidation stability, viscosity improvement andanti-wear properties to the composition. The base oil employed was asolvent refined naphthenic oil having an API gravity of 35, a flashpoint, COC, of 210 F., a kinematic viscosity at F. of 3.48 and aneutralization number of 0.01. A composition comprising a mixture ofmethyl and ethyl methacrylate polymers in the form of a 50% concentratein a white oil was added to this base oil to improve viscositycharacteristics. Tricresyl phosphate was also added as an anti-wearagent. To this composition various corrosion and oxidation inhibitorswere added, including 2-benzothiazyl-N,N-diethyldithiocarbamate, and thecorrosiveness of the resulting compositions determined. The results aregiven in Table I below.

TABLE I Hydraulic oils OXIDATION-CORROSION STABILITY TEST Oil No i 2 3 45 6 7 8 Composition:

Hydraulic base oil M ethacrylate polymer concentrate.... 13

'Iricresyl phosphate 4-Methyl-2,G-ditertiarybutyl phenol. Zincdibutyldithiocarbamate.

Z-Mereaptob enzothiazole 2-Benzothiazyl-N,N-diethyldithiocaramate. Metial Wt. Change, rug/so. am:

Small Stain.

do Clean Dull, border no. Cd vSlightly grey" Used Oil Tests:

Neut. No. Rise 0.00 0.00 Appearance Original Original..

N: .do

Stained.-- Dull Clean.-- Clean..... do Do.

Dark... Slightly Original Original Dark Slightly darkdarkened ened;

The oxidation and corrosion stability test of the foregoing table isthat prescribed in specification MIL-O- 5606 for aircraft hydraulicfluids and is carried out in the following manner: 100 cc. of the oilunder test are placed in a large test tube fitted with a refluxcondenser and immersed in a bath maintained at 121.l C. Weighed metalstrips, one of copper, one of low carbon, non-carbon-bearing steel, oneof aluminum alloy, one of magnesium alloy and one of cadmium platedsteel, each about 1 inch square, are fastened together so that themagnesium and copper do nottouch and placed in the test oil. Dry air isbubbled through the oil at a rate of approximately liters per hourduring the test. At the end of 168 hours, the test is discontinued, theneutralization number of the oil determined, and the metal testspecimens examined and reweighed to determine the loss due to corrosion.

The data given in Table I show that 2-benzothiazyl-N,N-diethyldithiocarbamate imparted superior anticorrosiveness and equaloxidation resistance as compared with equal amounts ofZ-mercaptobenzothiazole to a medium viscosity oilcontaining otherinhibitors of the types commonly employed in such oils. Furthermore the2-benzothiazyl-N,N-diethyldithiocarbamate was found to be entirelycompatible with these other inhibitors either singly or in combinations,indicating that oils may be produced by use of the inhibitors of ourinvention having a superior tolerance of contamination with mostcommercial lubricating or. hydraulic oils. As shown by Table I, oilshaving outstandingly superior oxidationcorrosion stabilitycharacteristics were obtained by use of the inhibitor combinationcomprising 2-benzothiazyl- N,N-diethyldithiocarbamate and zincdibutyldithiocarbamate. No. deterioration in these properties resultedwhen 4-methyl-2,6-ditertiary-butyl phenol was added as a third componentof the inhibitor combination. Considerably less improvement inanticorrosiveness was obtained by the use. of inhibitorcombinationscomprising zinc dibutyldithiocarbamate or4-methyl-2,6-ditertiarybutylphenol with Z-mercaptobenzothiazole insteadof 2- benzothiazyl-N,N--diethyldithiocarbamate, while an inhibitorcombination comprising Z-mercaptobenzothiazole with both zincdibutyldithiocarbamate and 4-methyl-2,6- ditertiary-butyl phenolproduced an oil which failed to meet the MIL-O-S 606 oxidation-corrosionstability specifications.

In addition to the superior effectiveness ofZ-benzothiazyl-N,N-diethyldithiocarbamate. as compared with2-mercaptobenzothiazole on an equal Weight basis, it is possible toemploy larger amounts of the former to obtain still further eifectbecause of its higher solubility, amounting to. at least 0.1'percent byweight in a medium viscosity oil as compared with about 0.01 percent byweight for 2- mercaptobenzothiazole. Table II below shows the relativesolubilities of these two compounds in the hydraulic base oil employedin the oils of Table I. In making these measurements the inhibitor wasdissolved in the oil by heating the oil at F. and stirring for one hour.As soon as the solution had cooled to room temperature the turbidity wasmeasured by means of a potentiometer type photoelectric photometer,which, is sold under the trade name of Lumetron.

TABLE H Relative oil solubilitie ofZ-benzothiazyl-N,N-diethyldithiacarbamate and Z-mercaptobenzothiazoleAdditive Content, Wt. Percent 2 Benzothiazyl N,N diethyldithiocarbamate:

Cold appearance percent Lumetron turbidity,

Transmission. 2-Mercaptobenzothiazole:

Cold appearance... Lumetron Transmission.

turbidity, percent Clear.... Clear Clear.... Clear.... Clear. 97 97 9898 90.

Clean... Slightly Hazy... Opaque. 3Q 77 23.

1 Remained clear'indefinitely.

2 Upon standingfor? days, much of the additive settled out and large,needle-like crystals formed.

naphthalene, such as other .alkylated aromatic compounds or compounds ofdifferent types, as for example ethylene glycol distearate orsweatings-from oxidized. ,parafiin wax. The above additives may bepresent in varying amounts :according tonthe deflects to ;.be produced,suitably 0.1-1.0 percent by weight of the phenolic oxidation inhibitor,about 1-10 percent by weight of the sulfonate and about 0.05-1L0 percentby weight o'f'the pour depressant, although largeror smaller amounts maybe employed if desired.

While the above examples serve to illustrate. typical compositionsemploying our novel corrosion inhibitors, it is understood that theinvention is not to be limited thereto. It will be evident from theabovethat they may be employed equally well in other lubricating oilcompositions, such as cutting oils, turbine oils, and so forth.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be-made without departing from the spiritand scope thereof and, therefore, only such limitations should beimposedas are indicated in the appended claims.

We claim:

1. A hydrocarbon lubricating oil containing a corrosion inhibitingamount of a 2-benzothiazyl-N,N-dialkyldithiocarbamate.

2. A mineral lubricating oil containing a corrosion inhibiting amount of2-benzothiazyl-N,N-dialkyldithiocarbamate.

3. A mineral lubricating oil containing from about 5 0.005 to about 0.2percent byweight of 2-benzothiazyl- N,N-diethyldithiocarbamate.

4. A hydraulic oil comprising in major proportion a mineral lubricatingbase oil compounded with about 0.1-1.0 percent by weight-0f apolyvalent-rnetal salt of a dialkyldithiocarbamic acid, and about0005-02 percent by weight of 2-benzothiazyl-N,N-dialkyldithiocarbamate.

5. A hydraulic oil according to claim 4 wherein the polyvalent metalsalt is zinc dibutyldithiocarbamate.

6. A hydraulic .oila'ccording-to claim 5 wherein the2-benzothiazyl-N,N-dialkyldithiocarbamate is2-benzothiazyl-N,N-diethyldithiocarbamate.

7. A hydraulic .oil having substantially the following composition inpercentages byweight:

Phosphorus acid ester (1.1-1.0 Polyvalent metal diaikyldithiocarbamate0005-02 2-benzothiazyl N,N-dialkyldithiocarbamate 0005-02 Methacrylateester polymer 1-15 Mineral lubricating oil Balance 8. A hydraulic oilhaving substantially the following composition in percentages by weight:

Tricresyl phosphate 0.1-1.0 Zinc dibutyldithiocarbamate 0.1-0.52-benzothiazyl-N,N-diethyldithiocarbamate- 0.01-0.2 Methacrylate esterpolymer 3-10 Mineral lubricating oil Balance 9. A lubricating and rustpreventive composition comprising in major proportion a minerallubricating base oil compounded with about 1-10. percent by Weight of anoil-soluble petroleum sulfonate, and about .0.005-0.2 percentby weightof.,2 benzotl1iazylN,N-dialkyldithiocarbamate.

10. A lubricating and rust preventive composition according to claim 9,also. containing 0.1-1.0 percent by weight of a phenolic oxidationinhibitor.

11. A composition comprising in major proportion. a mineral lubricatingbase oil compounded with about 0.1-1.0 percent-by weight of4-n1ethyl-2,6-ditertiary butyl phenol, and about.0.005-0.1- percent byweight of .2 benzothiazyl N,N-dialkyldithiocarbamate.

12. A lubricating;andixrust preventivet oil. having substantially the.following composition in. percentages by *Weight:

Oil-soluble petroleum sulfonate 1-10 Phenolic oxidation inhibitor'0;1-1.'0 Alkylated aromatic pour depressant compound 0.05-1z02-'benzothiazyl-N,N-dialkyldithiocarbamate; 0005-031 "Minerallubricating oil Balance 13. A lubricating and rust preventive. oilhaving substantially the following composition in percentages by weight:

Calcium mahogany sulfonate 1-10 4-methyl-2,6-ditertiarybutylphenol 0.1-1.0

Naphthalene chlorinated wax condensation product 0.05-1.0

2-benzothiazyhN,N-diethyldithiocarbamate 0.005-0-1 Mineral lubricatingoil Balance 'with about 0.1-1.0 percent by weight of a phosphorus acidester, about'0.005-0.-2 percent by weight of a polyvalent metaldialkyldithiocarbamate, and about 0005-02 percentby weight ofa.21benzothiazyl-N,N-dialkyldithiocarbamate wherein each of the saidalkyl groups contains from 1 to 6 carbon atoms. 1

17. A lubricating oilcomposition comprising in major proportion amineral lubricating base oil compounded with about 1-10 percent byweight of an oil-soluble petroleum sulfonate, and about 0005-02 percentby weight of a 2-benzothiazyl-N,N-dialkyldithiocarbamate wherein each ofthe'said alkyl groupscontains from 1 to 6 carbon atoms.

18. A composition comprising in majorproportion a mineral lubricatingbase oil compounded with about 0.1-1.0 percent by weight of aphenolicoxidation inhibitor and about 0.005-01 percent by weight of a 2-benzothiazylN,N-dialkyldithiocarbamate whereiireach of the said alkylgroups contains from 1 to 6 carbon atoms.

19. A lubricating oil composition comprising in major proportion amineral lubricating base oil compounded with about 1-10 percent byweight of an oil-soluble petroleum sulfonate, about 0.1-1.0 percent byweight of a phenolic oxidation inhibitor and about 0.005-0.1 percent byweight of a 2-benzothiazyl-N,N dialkyldithiocarbamate wherein each ofthe said alkyl groups contains from 1 m6 carbon atoms;

20. A lubricating oil composition comprisinga major proportion of amineral lubricating oil and a corrosion inhibiting proportion of acompound having the formula:

v in which R1 and R2 are alkylradicals-having'from 2 to 5 carbon atoms.

21, A lubricating oil composition comprising a ma or In place of thebase oil employed in the above bydraulic oil compositions, othersuitable lubricating oils may be employed, such as different mineral oilfractions obtained from difierent types of crude oils or produced bydifferent refining methods, synthetic oils, and so forth. Furthermore,in place of or in addition to the other additives employed incombination with the inhibitors of our invention, compounds of similarnature or their recognized equivalents may be used. Thus, in place of 4-mcthyl-Z,6-ditertiary-butyl phenol, compositions of the above type maycontain other phenolic oxidation inhibitors, particularly thetri-alkylated phenols containing sufiicient alkyl carbon atoms topromote oil solubility, such as for example 2,4,6-tritertiary-butylphenol, 2-isopropyl-4,6-dimethyl phenol and 2,6-ditertiary-butyl-4-tertiary-amyl phenol. In place of zinc dibutyldithiocarbamate, thesecompositions may contain other compounds of the class comprising metalsalts of dialkyldithiocarbamic acids, as disclosed for example byDenison et al., U. S. Patent 2,394,536. Salts of a dialkyldithiocarbamicacid with a polyvalent metal such as calcium or zinc are preferred forthis purpose. These are suitably employed in amounts ranging from about0.1 to 1.0 percent by weight. The tricresyl phosphate may be substitutedby another suitable ester of phosphoric or phosphorous acid or by adifferent type of anti-wear agent such as dibenzyl disulfide. Also, inplace of the methacrylate polymer other suitable materials for improvingthe viscosity and viscosity index characteristics may be employed suchas other polymeric materials or condensation products for exampleisobutylene polymer. The viscosity improvers are generally employed in aproportion of about 1-15% by weight (basis the polymer).

Still further in accordance with our invention a lubricating andpreservative composition especially suitable as an aircraft instrumentoil was developed by the use of2-benzothiazyl-N,N-diethyldithiocarbamate in a medium viscosity oil. Thebase oil employed was a blend comprising 71 percent by weight of ahighly sulfur dioxide refined naphthenic type distillate oil having anSUS viscosity at 100 F. of about 50 and 29 percent by weight of a sulfurdioxide refined naphthene base distillate oil having an SUS viscosity at100 F. of about 100. Other additives were employed comprising a rustinhibitor, an oxidation inhibitor and a pour depressant, the latterbeing an alkylated naphthalene obtained by reacting naphthalene withchlorinated wax in the presence of aluminum chloride and commerciallyavailable under the trade name The above oil very satisfactorily met allthe requirements of Army-Navy specification AN-O-6a, Amendment-4(February '19, 1948) for general purpose, low temperature lubricatingoils. Table III below shows the corrosion and oxidation stability andthe corrosion protection properties of this composition, designated oilNo. 9, against the requirements of the said Army-Navy spec ification.

6 TABLE HI General purpose, low temperature lubricating oilOXIDATION-CORROSION STABILITY AND CORROSION PREVENTION TESTS metals.Appearance V Slight discoloraation permissible.

Oxidation:

Vis. change, C. S. at F., 5 to +20.

percent of original. N eut. N 0. increase 0.20 Max. Separation ofinsoluble None.

materials. Gumming do Do. Weight loss, percent 1 5 Max. CorrosionProtection:

Humidity Cabinet Test, hrs. ggh g gf' }100 Min.

The oxidation and corrosion test results of the foregoing table wereobtained by the oxidation and corrosion stability test as described inconnection with Table I.

The humidity cabinet test of the foregoing table is a test fordetermining the amount of protection afforded. to steel surfaces by anoil under rusting conditions. Two clean, non-copper-bearing steelpanels, each two inches by four inches by inch thick, are employed inthis test. These are dipped in the test oil at room temperature (77 F),allowed to drain for 2 hours at the same temperature and then suspendedin a humidity cabinet maintained at F. The air in thecabinet issaturated.

with water vapor at this temperature, so that continuous- The panels arecondensation occurs upon the panels. examined every 24 hours forevidence of corrosion. The oil is considered as having passed the testif, at the end of 100 hours neither of the panels shows more thana traceof corrosion, defined as not more than three small spots no one of whichis more than one millimeter in: diameter.

Table III shows that the corrosion inhibitors of our invention impartexceptional rust preventing properties in addition to excellentoxidation and corrosion stability properties to hydrocarbon oils. Thesuperior effective ness of these compounds in imparting anti-rustingproperties to hydrocarbon oils is demonstrated by the fact: that acomposition identical with oil No. 9 of the above: table with theexception that an equal weight of 2-mer-- captobenzot-hiazole wassubstituted for the 2-benzothiazyl- N,N-diethyldithiocarbamate gave only240 hours of pro-- tection in the humidity cabinet test.

In place of the oil base employed in oil No. 9 described above, otherlubricating oil fractions may be em-- ployed as discussed in connectionwith the oils of Table I. Likewise other additives of similar functionmay be substituted for those employed in combination with the inhibitorsof our invention. For example, in place of 4- methyl-2,6-ditertiarybutyl phenol, other phenolic oxidation inhibitors may be employed asdiscussed above. In place of calcium mahogany sulfonate, otheroil-soluble sulfonic acid salts may be employed which may be ob tainedfrom different sulfonic acids or by neutralizing sulfonic acids withsuitable compounds of various other metals such as the oxides orhydroxides of sodium, potassium, ammonium, barium, aluminum, etc.Different pour depressors may also be employed in place of the alkylatedproportion of a mineral lubricating oil and a corrosion inhibitingproportion of a compound having the formula:

in which R1 and R2 are alkyl radicals.

References Cited in the file of this patent UNITED STATES PATENTSTeppema Sept. 14, 1936 Miller et a1. Nov. 21, 1944 Bergen Jan. 30, 1945Ross et a1. Mar. 13, 1945 Bergen Oct. 2, 1945 Miller et a1 Dec. 17, 1946Ritter et a1. Oct. 3, 1950

1. A HYDROCARBON LUBRICATING OIL CONTAINING A CORROSION INHIBIDINGAMOUNT OF A 2-BENZOTHIAZYL-N-DIALKYLDITHIOCARBAMATE.